Mon. Not. R. Astron. Soc. 000, 1–26 (2015) Printed 12 September 2018 (MN LATEX style file v2.2) Kinematics and Mass Modeling of M33: Hα Observations Kam, Z. S.1;2;3?, Carignan, C.1;2;3, Chemin, L.4, Amram, P.5 & Epinat, B.5 1Laboratoire d’Astrophysique Expérimentale, Département de physique, Université de Montréal, C.P. 6128, Succ. centre-ville, Montréal, Québec, Canada, H3C 3J7 2Observatoire d’Astrophysique de l’Université de Ouagadougou, BP 7021, Ouagadougou 03, Burkina Faso 3Department of Astronomy, University of Cape Town, Private Bag X3, Rondebosch 7701, South Africa 4Université de Bordeaux & CNRS, LAB, UMR 5804, F-33270, Floirac, France 5 Université Aix Marseille , CNRS, LAM (Laboratoire d’Astrophysique de Marseille), 13388, Marseille, France 12 September 2018 ABSTRACT As part of a long-term project to revisit the kinematics and dynamics of the large disc galaxies of the Local Group, we present the first deep, wide-field (∼ 420 × 560) 3D-spectroscopic survey of the ionized gas disc of Messier 33. Fabry-Perot interfer- ometry has been used to map its Hα distribution and kinematics at unprecedented 00 angular resolution (.3 ) and resolving power (∼ 12600), with the 1.6 m telescope at the Observatoire du Mont Mégantic. The ionized gas distribution follows a com- plex, large-scale spiral structure, unsurprisingly coincident with the already-known spiral structures of the neutral and molecular gas discs. The kinematical analysis of the velocity field shows that the rotation center of the Hα disc is distant from the photometric center by ∼ 170 pc (sky projected distance) and that the kinematical major-axis position angle and disc inclination are in excellent agreement with photo- metric values. The Hα rotation curve agrees very well with the Hi rotation curves for 0 < R < 6:5 kpc, but the Hα velocities are 10 − 20 km s−1 higher for R > 6.5 kpc. The reason for this discrepancy is not well understood. The velocity dispersion profile is relatively flat around 16 km s−1, which is at the low end of velocity dispersions of nearby star-forming galactic discs. A strong relation is also found between the Hα velocity dispersion and the Hα intensity. Mass models were obtained using the Hα rotation curve but, as expected, the dark matter halo’s parameters are not very well constrained since the optical rotation curve only extends out to 8 kpc. Key words: techniques: interferometric, integral field, Fabry-Perot – galaxies: indi- vidual: M33 – galaxies: kinematics and dynamics – galaxies: ISM: Bubbles, HII regions – cosmology: dark matter arXiv:1503.02538v1 [astro-ph.GA] 9 Mar 2015 1 INTRODUCTION parts and sensitive lower spatial resolution Hi observations in the outer parts to derive the most accurate mass mod- Late-type spiral and dwarf irregular (dIrr) galaxies present els for the luminous disk and the dark halo. The objective an extended H emission. The H emission usually extends i i of this project is to perform a new mass distribution model to larger radii than the optical emission. This makes of H i of Messier 33 (M33), combining high-sensitivity Hα and HI a powerful tool for probing the dark matter (DM) domi- interferometric data. In particular, this article presents the nated regions and for characterizing the parameters of the first Hα survey devoted to the large-scale distribution and flat part of the rotation curves (RCs). However, it is the ris- kinematics of the M33 ionized gas disk. ing inner part of the RCs that constrains the parameters of the mass models (see e.g. Blais-Ouellette et al. 1999). Two- M33 is the second most luminous spiral (SA(s)cd) dimensional Hα observations are ideally suited to give more galaxy in our neighborhood after M31. With an absolute accurate velocities in the inner parts of galaxies having a magnitude of MV ∼-19.3, it presents several arms (Sandage better spatial resolution than the Hi (Amram et al. 1992, & Humphreys 1980). Although two main arms are well 1994; Swaters et al. 2000). The ideal approach is then to known, M33 has not a clearly defined grand-design pattern. combine high spatial resolution Hα observations in the inner A system of seven spiral arms is pointed out by Ivanov & Kunchev (1985). In the optical bands, it could be consid- ered as a flocculent spiral galaxy, but UV and IR observa- ? E-mail:[email protected] tions show more prominent arms. The M33 profile presents c 2015 RAS 2 Kam et al. Table 1. Optical parameters of M 33. Cockcroft et al. (2013) and Wolfe et al. (2013) around M31 and M33 can only be explained by these interactions. Deep Parameter Value Source Hα observations of M33 reveal the presence of low density Morphological type SA(s)cd RC3 Hii regions outside the optical disk (Hoopes et al. 2001). h m s R.A. (2000) 01 33 33.1 RC3 This suggests recent star formation activity, possibly due to o 0 00 Dec. (2000) +30 39 18 RC3 recent interactions. ◦ ◦ Optical inclination, i 52 ±3 WW Studying the kinematics of such a galaxy will provide Optical major axis, PA 22.5◦±1◦ WW a better understanding of the contribution of dark matter Apparent magnitude, m 5.28 RC3 V and of the best functional form describing its distribution. Absolute magnitude, MV -19.34 (J-K) 0.89 JTH Still today, the cusp–core problem remains as one compares 0 Optical radius, R25 ( ) 35.4 ± 1.0 RC3 observations to predictions, especially for dwarf systems and −1 Systemic velocity, Vsys -179 ±3 km s RC3 this, despite the numerous studies on the DM distribution in References:WW: Warner et al. (1973), RC3: de Vaucouleurs galaxies in the last 30 years. While, on large scales, N-body et al. (1991), JTH: Jarrett et al. (2003) cosmological simulations reproduce well the observations, it is more problematic at galaxy scales. The NFW profile, de- Table 2. Distances for M 33. rived from those simulations, predicts a cuspy distribution in the central parts of the DM halos (e.g. Fukushige & Makino Method Distance Modulus Distance Source 1997; Moore et al. 1999; Navarro et al. 1997, 2010; Ishiyama (indicator) m-M [mag] [Mpc] et al. 2013), while observations especially of dwarf systems TRGB 24.54 ± 0.06 0.81 (1) TRGB 24.75 ± 0.10 0.89 (2) show more a core distribution (Oh et al. 2011). Those re- TRGB 24.64 ± 0.15 0.85 (3) sults can be explained by the gravitational potential related PNLF 24.62 ± 0.25 0.84 (4) to the gas in those simulations, since the gas, which is impor- Cepheids 24.64 ± 0.06 0.85 (5) tant in the inner parts, is not accurately introduced in those Cepheids 24.70 ± 0.13 0.87 (6) simulations. Phenomena such as stellar feedbacks, galactic Cepheids 24.52 ± 0.14 0.80 (7) winds or massive clumps are not often well handled and re- Cepheids 24.55 ± 0.28 0.81 (8) produced (Goerdt et al. 2010; Inoue & Saitoh 2011; Ogiya & Cepheids 24.58 ± 0.10 0.84 (9) Mori 2011; Pontzen & Governato 2012; Teyssier et al. 2013). Cepheids 24.62 ± 0.01 0.84 (10) Several studies of the kinematics of M33 exist (e.g. Cor- Mean adopted distance 0.84 ±0:04 100 ≡ 4 pc belli & Salucci 2000; Corbelli 2003; Putman et al. 2009; Cor- References: (1) McConnachie et al. (2005), (2) Stonkut˙eet al. belli et al. 2014), mainly based on Hi. It appears from those (2008), (3) Galleti et al. (2004), (4) Magrini et al. (2000), (5) studies that M33 is dark matter dominated (the dark mat- Saha et al. (2006), (6) Paturel et al. (2002), (7) McConnachie ter mass is > 10 times larger than the mass of the stellar et al. (2004), (8) An et al. (2007), (9) Freedman et al. (2001), disk) and that its Hi disk is strongly warped. The gas in the 9 (10) Gieren et al. (2013) disk of M33 is estimated ∼1.4-3×10 M (Corbelli 2003; Putman et al. 2009). In the mass model derived by Corbelli 9 a small bulge-like component in the IR bands. Its bulge and (2003), the stellar mass is estimated at ∼ 3−6×10 M and 10 nucleus are the subject of numerous studies (e.g.: McLean & the dark halo mass at ∼5×10 M . Most of the M33 kine- Liu 1996; Lauer et al. 1998; Gordon et al. 1999; Corbelli & matical studies use Hi or CO (H2), with a probable beam Walterbos 2007). The optical parameters of M33 are given smearing impact on the innermost parts of the RC due to the in Table 1. lower spatial resolution of the Hi data. Among the few Hα In the literature, one can find distances to M33 varying (optical) studies, the results presented by Carranza et al. from 700 to 940 kpc. Table 2 gives recent distance mea- (1968) show small velocity dispersions from 5 km s−1 to surements for M33. The adopted distance for this study 9 km s−1 in the disk. However, they argue that these values is D = 0.84 Mpc (scale 1’ = 244 pc). It is the mean dis- could even be lower if taking into account the instrumental tance estimated by using resolved sources techniques such as corrections. The mass-to-light ratio is an important param- Cepheids, Planetary Nebulae Luminosity Function (PNLF) eter in the determination of the dark matter halo shape. In and Tip of the Red Giant Branch (TRGB). The optical disk M33, Boulesteix & Monnet (1970) show very low values of of M33 has a scale length of ∼9.20 (2.25 kpc) in the V band M/L in the central (< 500) part of the galaxy and increasing (Kent 1987; Guidoni et al.